1. Field of the Invention
The present invention relates to a method of screening a semiconductor laser device and, more particularly to a method of screening capable of rejecting a semiconductor laser device which fails due to sudden deterioration.
2. Description of the Prior Art
FIG. 3 shows the result of an endurance test of InGaAs/AlGaAs semiconductor laser devices conducted by G. Beister et al. (G. Beister et al. "Monomode emission at 350 mW and high reliability with InGaAs/AlGaAs (.lambda.=1020 nm) ridge waveguide laser diodes", Electron. Lett., vol.34, pp.778-779, 1998). The endurance test was conducted under conditions of constant ambient temperature of 40.degree. C. for the semiconductor laser device with such a driving current that produces constant optical output of 300 mW being supplied. In the drawing, numeral 101 denotes an initial failure device, 102 denotes a sudden failure device, 103 denotes device showing stable operation. Among ten devices subjected to the endurance test, seven devices (103) showed stable operation over 1000 hours. Two (101) of the ten devices showed initial failure with the operating current increasing at an early stage, and the remaining one (102) showed sudden failure without prior sign of deterioration. While the sudden failure in this test occurred after 180 hours of operation, sudden failures in general can take place at any time.
With a method of screening of the prior art which is conducted by keeping a constant optical output of semiconductor laser devices, for example, initial failure devices (101) can be rejected but sudden failure devices (102) cannot be rejected. Consequently, there has been a limitation to decreasing of failure rate of final products which have passed screening, resulting in such a problem that the devices cannot be used in the field of communication which requires high reliability.
The present inventors have found that the sudden failures are caused mainly by the breakdown of the active layer of the semiconductor laser device due to the migration of crystalline defects. The present inventors have also found that sudden failure of devices due to such crystal defects can be removed by screening semiconductor laser devices while supplying a driving current to the semiconductor laser devices and applying thermal cycles thereto, thus completing the present invention.